1. Field of the Invention
The present invention relates to an optical disc apparatus for performing tracking control according to a phase difference between detection signals.
2. Description of the Related Art
A differential phase detection (DPD) method is employed as a tracking signal detecting method for reproducing a signal of an optical disc such as digital versatile disc (DVD) or high definition-digital versatile disc (HD DVD). This method is for detecting a temporal shift between pit positions of optical detection cells divided into the right and left of a tracking and for detecting a tracking positional shift (Jpn. Pat. Appln. KOKAI Publication No. 2005-182927).
In a next-generation optical disc, high definition digital versatile disc (HD DVD), an optical spot becomes relatively larger for a recording signal (that is, pit or mark/space) due to high density of information recording so that a degree of modulation of a mark/space signal with short time becomes smaller. Thus, it becomes difficult to detect a temporal shift of data positions between the divided light receiving cells. In other words, the shorter a data length of a recording signal is, the less a resolution of a detection signal thereof is, and a resultant phase difference signal (signal for detecting a temporal shift) in the DPD method includes more errors. Further, in a high-speed reproduction, since the faster the speed is, the smaller an absolute value of the temporal shift to be detected is, a propagation delay or relative detection delay of a detection signal occurs in a signal where a data length of a recording signal is short, and the detected phase difference signal includes more errors. Therefore, the higher the density of the optical disc is and the shorter the data length of the recording signal is, and the faster the reproduction speed is, the more difficult it is to detect a tacking positional shift.